VOLUME DEPENDENCE OF THE A(1G) PHONONS IN YBA2CU3O7

By employing first-principles frozen-phonon calculations we have deter mined the force-free geometry and the dynamical matrix for the five Ra man-active A(1g) modes in a volume-reduced YBa2Cu3O7 crystal. By this mean we investigate the relation between the effect of overbinding cau sed by the local density approximation and the vibronic properties of this material. This procedure reveals noticeably improved phonon frequ encies in comparison to the theoretical results obtained for the measu red lattice constants.